/*
 * Copyright (C) 2013 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.collect.CollectPreconditions.checkEntryNotNull;

import com.google.common.annotations.GwtIncompatible;
import javax.annotation.Nullable;

/**
 * Implementation of {@code Map.Entry} for {@link ImmutableMap} that adds extra methods to traverse
 * hash buckets for the key and the value. This allows reuse in {@link RegularImmutableMap} and
 * {@link RegularImmutableBiMap}, which don't have to recopy the entries created by their
 * {@code Builder} implementations.
 *
 * <p>
 * This base implementation has no key or value pointers, so instances of ImmutableMapEntry (but not
 * its subclasses) can be reused when copied from one ImmutableMap to another.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible // unnecessary
class ImmutableMapEntry<K, V> extends ImmutableEntry<K, V> {
    /**
     * Creates an {@code ImmutableMapEntry} array to hold parameterized entries. The result must
     * never be upcast back to ImmutableMapEntry[] (or Object[], etc.), or allowed to escape the
     * class.
     */
    @SuppressWarnings("unchecked") // Safe as long as the javadocs are followed
    static <K, V> ImmutableMapEntry<K, V>[] createEntryArray(int size) {
        return new ImmutableMapEntry[size];
    }

    ImmutableMapEntry(K key, V value) {
        super(key, value);
        checkEntryNotNull(key, value);
    }

    ImmutableMapEntry(ImmutableMapEntry<K, V> contents) {
        super(contents.getKey(), contents.getValue());
        // null check would be redundant
    }

    @Nullable
    ImmutableMapEntry<K, V> getNextInKeyBucket() {
        return null;
    }

    @Nullable
    ImmutableMapEntry<K, V> getNextInValueBucket() {
        return null;
    }

    /**
     * Returns true if this entry has no bucket links and can safely be reused as a terminal entry
     * in a bucket in another map.
     */
    boolean isReusable() {
        return true;
    }

    static class NonTerminalImmutableMapEntry<K, V> extends ImmutableMapEntry<K, V> {
        private final transient ImmutableMapEntry<K, V> nextInKeyBucket;

        NonTerminalImmutableMapEntry(K key, V value, ImmutableMapEntry<K, V> nextInKeyBucket) {
            super(key, value);
            this.nextInKeyBucket = nextInKeyBucket;
        }

        @Override
        @Nullable
        final ImmutableMapEntry<K, V> getNextInKeyBucket() {
            return nextInKeyBucket;
        }

        @Override
        final boolean isReusable() {
            return false;
        }
    }

    static final class NonTerminalImmutableBiMapEntry<K, V> extends NonTerminalImmutableMapEntry<K, V> {
        private final transient ImmutableMapEntry<K, V> nextInValueBucket;

        NonTerminalImmutableBiMapEntry(K key, V value, ImmutableMapEntry<K, V> nextInKeyBucket,
                ImmutableMapEntry<K, V> nextInValueBucket) {
            super(key, value, nextInKeyBucket);
            this.nextInValueBucket = nextInValueBucket;
        }

        @Override
        @Nullable
        ImmutableMapEntry<K, V> getNextInValueBucket() {
            return nextInValueBucket;
        }
    }
}
